This invention is directed to a low frictional connection between two elements of the type wherein one is capable of rotation with respect to the other. A low frictional surface is formed on a helical member and inserted between the two elements. A bearing riding against this low frictional surface provides for a low frictional connection between the two elements. The helical member is capable of being easily replaced should its low frictional surface be compromised in any manner.
With the development of engines, motors, transmissions and other similar mechanical elements which utilize rotating shafts, cranks, and the like, the need for low frictional connections between such rotating shafts and their support and/or elements connected to them, has led to the development of two major types of bearings. These two types are sliding bearings and roller bearings.
Both sliding bearings and roller bearings require smooth machined surfaces to work against. This in the internal combustion engine working attachment of the connecting rods to the crankshaft requires machining to tolerances of each of the crankpin journal surfaces to which the connecting rod connects as well as the same treatment on the main bearing journal surfaces on the crankshaft wherein the crank is supported within the engine case. When sliding bearings are utilized to connect either the connecting rod to the crankshaft or the crankshaft to the case, the sliding bearing is usually of the type having a split cylindrical bushing, sleeve or insert located around the machined journal surface. On the connecting rods the inserts are held in place against motion by an appropriate opening formed in part of the connecting rod and in part in a rod cap fitting on the end of the rod. The main bearing bushings are also held captive in appropriate openings in the matching parts of the engine case to prevent motion.
In smaller engines, typically needle bearings are used to provide an anti-friction bearing surface between the crankshaft and the connecting rod or engine case. The needle bearings reduce weight and provide for a through flow of lubricant between the crankshaft and the inside of the connecting rod journal or bearing race parallel to the needle rollers. When needle bearings are used the line of contract provides such operating loads that the contact surfaces of the crankshaft, connecting rod or bearing race must be hardened and ground. Hardening of the contact surfaces on the crankshaft usually requires copper plating of the whole crankshaft then a grinding through the copper in only those regions where the hardening is to take place. This is then followed by a final finish grind. This results in a shaft which is partially ductile and partially hardened. The resultent boundary line between these two conditions represents the ultimate failure line for the crankshaft.
Bearing races and to an extent the connecting rod and its cap are inexpensive to produce and harden compared to crankshafts for the following reasons. Only one anti-friction surface needs to be formed on the bearing race or within the connecting rod and its cap. If for some reason during manufacture or during use this surface is catastrophically destroyed by marring, undersizing or the like the race or connecting rod could be disposed of without incurring too great an economic loss. Crankshafts, on the other hand, contain a plurality of journal surfaces. The crankshaft is initially forged or built up and then the journal surfaces must be hardened and machined. A typical four cylinder engine would require the crankshaft to have four journal surfaces for the connecting rods and at least two but more commonly three surfaces for the main bearings wherein the crankshaft is supported in the case. Thus at a minimum six surfaces must be hardened and machined on a typical four cylinder engine crankshaft. If during machining one of these surfaces is catastrophically destroyed for one reason or the other the whole crankshaft is rendered useless. The unuseable surface may be the first surface machined or it may be the sixth surface or any surface inbetween. If it is the second to the sixth surface, of course, all prior work in machining the previous surfaces is all for naught. Having to scrap a partially prepared crankshaft is a very expensive endeavor for the manufacturer.
Aside from manufacturing it is also sometimes necessary to regrind the journal surfaces of crankshafts in repairing engines. Such regrinding requires removal of a portion of the journal surface. It is, of course, evident that there is a limit to the amount of material that can be ground off of this journal surface. For reasons of strength and dynamic balance any particular journal surface must be within certain tolerances with the other surfaces. This then forms a situation exactly analogous to the manufacturer's situation noted above.
In view of the above it is evident that there exists a need for new and improved low frictional connections between rotating mechanical elements such as a crankshaft and a connecting rod. Further, it is considered that there exists a need for new and improved low frictional connection between elements which increases the lubrication at the contact points between said elements and thus even further reduces the frictional forces between the elements as they rotate. It is also considered that there exists a need for forming a hardened ground surface on the journals of crankshafts such that the surface on each individual journal of a multiple journal crankshaft can be individually and independently prepared or replaced. Additionally, it is considered that there exists a need for a crankshaft having homogeneous malleability throughout while still including hardened surfaces on its journals.